1. Field of the Invention
The present invention relates to a capacitor and a method of manufacturing the same and, more particularly, a capacitor having a ferroelectric layer or a high-dielectric layer and a method of manufacturing the same.
2. Description of the Related Art
A high-dielectric layer such as a BST ((Ba,Sr)TiO3) layer, an ST (SrTiOx) layer, a Ta2O5 layer, etc. and a ferroelectric layer such as a PZT (PbZrxTi1−xO3) layer, etc., are widely used as a capacitor dielectric layer in a DRAM (Dynamic Random Access Memory), a FeRAM (Ferroelectric Random Acces Memory), etc., by employing positively a high dielectric constant and an inverted polarization characteristic.
Also, in a ferroelectric capacitor of FeRAM, a planar-type capacitor having a structure in which a connection between the lower electrode of the capacitor and the impurity diffusion region of the transistor is extracted from the upper side of the lower electrode is practically used. In this case, a stacked-type capacitor having a structure in which the lower electrode is connected to the impurity diffusion region via the conductive plug formed immediately under the lower electrode is required in the future to reduce cell area.
If the high-dielectric oxide layer or the ferroelectric oxide layer is used as the capacitor dielectric layer, platinum (Pt) is widely used as the electrode material. This is because the conductivity of the platinum is high, platinum can withstand the high-temperature process in the course of formation of the dielectric layer, and platinum can control the orientation direction of the capacitor dielectric layer formed thereon, etc.
On the contrary, platinum has high oxygen permeability. Therefore, if the lower electrode made of platinum is formed on the plug in the stacked-type capacitor, oxygen can transmit through the lower electrode in the annealing process in the course of the formation of the capacitor dielectric layer to oxidize the plug. As a result, for example, if the plug is formed of tungsten, an insulating tungsten oxide layer is formed between the plug and the lower electrode and, thus, contact between the plug and the lower electrode is lost.
Therefore, in the stacked-type capacitor, the stacked structure such as e Pt/Ir structure in which the Ir layer and the Pt layer are formed sequentially from the bottom, the Pt/IrO2 structure in which the IrO2 layer and the Pt layer are formed sequentially from the bottom, the Pt/IrO2/Ir structure in which the Ir layer, the IrO2 layer, and the Pt layer are formed sequentially from the bottom, or the like, is employed as the lower electrode structure.
The iridium (Ir) layer and the iridium oxide (IrO2) layer has a very small oxygen permeability and acts as an oxygen barrier in the annealing process. Therefore, if this layer is formed as the underlying layer of the platinum layer serving as the lower electrode of the stacked-type capacitor, oxidation of the plug under the lower electrode can be prevented in the course of the formation of the capacitor dielectric layer.
For example, in Patent Application Publication (KOKAI) Hei 9-22829, it is proposed to use the Pt/IrO2/Ir structure as the lower electrode of the ferroelectric capacitor having the stacked structure. This structure succeeds in assuring the desired characteristic of the ferroelectric layer, while suppressing the oxidation of the lower layer structure of the capacitor by the annealing process in the oxygen atmosphere.
However, in the case that the PZT layer deposited by a sputtering method is applied as the capacitor dielectric layer, it is found that, if the lower electrode structure containing the iridium-based oxygen barrier layer (Ir layer, IrO2 layer) is employed, an increase in the leakage current of the capacitor is brought about.
If the PZT layer is deposited on the lower electrode by sputtering, the as-deposited PZT layer is in an amorphous state and a high-temperature annealing process is needed to crystallize the PZT layer.
However, if the high-temperature annealing process is applied to crystallize the PZT layer after the amorphous PZT layer is deposited on the lower electrode having the structure in which the Pt layer is formed on the iridium-based oxygen barrier layer, the iridium element in the iridium-based oxygen barrier layer transmits through the Pt layer to diffuse into the PZT layer and then is introduced into the PZT crystal. As a result, the insulating property of the PZT crystal is lowered.
Such phenomenon can be avoided by growing the PZT layer that is in the crystal state on the lower electrode or crystallizing the PZT crystal at the low temperature. In this case, the dielectric constant of the formed PZT layer becomes small.